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FOCUS ON FIREFIGHTER PHYSIOLOGY

PHYSIOLOGICAL RECOVERY FROM FIREFIGHTING ACTIVITIES IN

REHABILITATION AND BEYOND

Gavin P. Horn, PhD, Steve Gutzmer, BS, Christopher A. Fahs, MS, Steve J. Petruzzello, PhD,Eric Goldstein, BS, George C. Fahey, PhD, Bo Fernhall, PhD, Denise L. Smith, PhD

ABSTRACT

Objectives. The primary objective of this study was to doc-ument the timeline of physiologic recovery from firefight-ing activities in order to inform emergency medical services(EMS) of vital sign values that might be expected during in-cident rehabilitation and in developing rehabilitation proto-cols to make decisions about when to return personnel tothe fireground. Secondarily, we compared two different in-cident rehabilitation strategies to determine effectiveness inreducing physiologic strain following firefighting. Methods.A repeated-measures randomized crossover design was uti-lized in which firefighters conducted a controlled set of fire-fighting activities, after which they completed incident re-habilitation in one of two conditions: 1) similar to currentlyused rehabilitation protocols and 2) with active cooling andnutritional intervention. Following 15 minutes of rehabilita-tion, each firefighter was asked to perform a simulated res-cue “dummy drag” and then recover for 120 minutes in aquiet area. Core temperature and heart rate were recordedthroughout the study. Blood pressures and subendocardialviability ratios were obtained before firefighting, after fire-fighting, and at standardized times during rehabilitation and

Received April 20, 2010, from the University of Illinois (GPH, SG,CAF, SJP, EG, GCF, BF, DLS), Champaign, Illinois; the Univer-sity of Oklahoma (CAF), Norman, Oklahoma; Georgetown Univer-sity (EG), Washington, DC; and Skidmore College (DLS), SaratogaSprings, New York. Revision received September 25, 2010; acceptedfor publication September 27, 2010.

Supported by the National Institute for Occupational Safety andHealth (1R03 OH009111–01).

The authors thank the volunteers in this study for their participationand also acknowledge Sue Blevins for her assistance with data entryand test preparations.

The authors report no conflicts of interest in this study.

Address correspondence and reprint requests to: Gavin Horn, PhD,University of Illinois Fire Service Institute, 11 Gerty Drive, Cham-paign, IL 61820. e-mail: [email protected]

doi: 10.3109/10903127.2010.545474

recovery. Results. Heart rate and core temperature increasedduring firefighting, and core temperature continued to in-crease for 7 minutes after completion of firefighting activ-ities. These values did not return to baseline until at least50 minutes after firefighting activity. Systolic blood pressureswere significantly reduced during rehabilitation (15.2%), andrecovered 7.7% during the first 50 minutes of recovery, butremained significantly lower than before firefighting for atleast 120 minutes. An index of subendocardial perfusionwas also significantly depressed for up to 110 minutes af-ter firefighting. Differences between rehabilitation protocolswere minimal. Conclusions. The timeline for recovery fromfirefighting activities is significantly longer than the typi-cal 10–20-minute rehabilitation period that often is providedon the fireground. Modifications from the current rehabili-tation protocol do not appear to improve the recovery time-line when rehabilitation is conducted in a cool room. Whilefirefighters often are concerned about elevated blood pres-sures, this study suggests that firefighters and EMS person-nel should also be cognizant of the potential dangers of hy-potension. Key words: rehabilitation; blood pressure; bodytemperature; heart rate; firefighter

PREHOSPITAL EMERGENCY CARE 2011;15:214–225

INTRODUCTION

Emergency medical services (EMS) personnel are com-monly dispatched to the scene of a working fire to sup-port fireground incident rehabilitation practices. How-ever, little fact-based evidence has been provided toEMS or fire personnel to determine typical vital signsof a firefighter who is recovering from a bout of strenu-ous fireground activity. As such, there are few scientif-ically based indicators to support decisions to release afirefighter, to hold firefighters from activity, or when totransport firefighters to the hospital.1

Each year, approximately 100 firefighters lose theirlives in the line of duty and tens of thousands are in-jured. Over the past 10 years, approximately 40–50%of line-of-duty deaths have been attributed to heartattacks.2 Another 650–1,000 firefighters suffer from

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Horn et al. FIREFIGHTER REHABILITATION AND RECOVERY 215

nonfatal heart attacks in the line of duty each year.3 It iswell recognized that firefighting leads to increased car-diovascular and thermal strain.4,5 However, the timecourse of recovery from firefighting is not well docu-mented despite the fact that a large percentage of fire-fighting fatalities occur shortly after firefighting activi-ties have ended.6

Incident rehabilitation has been broadly recom-mended to mitigate the cardiovascular and thermalstrain associated with performing strenuous firefight-ing activity. While there has been some effort to un-derstand the effect of different cooling strategies onfirefighters’ tolerance time and core temperature,7,8 theefficacy of different nutritional interventions has notbeen documented, despite the fact that the NationalFire Protection Association (NFPA) has specific rec-ommendations regarding the provision of nutrition.Finally, during rehabilitation, medical monitoring usu-ally consists of collection of traditional vital signs suchas heart rate and blood pressure. However, central aor-tic blood pressure may be a better predictor of clincialoutcome than brachial pressure,9,10 and with currenttechnology this measurement can be implemented in arehabilitation unit if found to be useful.

The purpose of this study was to describe the acuteeffects of firefighting on traditional vital signs as wellas several novel vascular measures (e.g., central aor-tic blood pressure, subendocardial viability ratio) andto document the time course of recovery. Addition-ally, we compared two incident rehabilitation strate-gies (control and enhanced) to determine the extent towhich an “enhanced” rehabilitation might facilitate re-covery from firefighting activities.

METHODS

Human Subjects

Local career and volunteer male firefighters betweenthe ages of 19 and 39 years were recruited to participatein this study. Prior to participation in the testing, theparticipants completed a health history questionnaire.Firefighters who indicated that they had a diagnosedhistory of atherosclerotic cardiovascular disease, weretaking medications for high blood pressure or choles-terol, or were taking aspirin, acetaminophen, ibupro-fen, or cold or asthma medications were excluded fromparticipating in the study.

Participants were fully informed of the purpose ofthe study, were provided with an opportunity to askquestions of the investigators, and were informed ofthe requirements of participation. Participants signedan informed consent document indicating that theyunderstood the risks and benefits of participation andthat their participation was voluntary. This study wasapproved by the University of Illinois Institutional Re-view Board.

Study Design

Twenty-three firefighters were recruited to participatein a within-subject, randomized, repeated-measuresstudy designed to investigate the time course of recov-ery from strenuous firefighting and the effectiveness ofincident rehabilitation interventions. The repeated re-habilitation trials were separated by a minimum of 48hours and administered in a counterbalanced fashionto ensure that half of the participants received the con-trol condition first and half of the participants receivedthe enhanced condition first. Of the 23 enrolled sub-jects, 21 firefighters completed both trials of the study.Two subjects did not complete both trials: one becauseof a prolonged illness and the other because of a work-place injury (not related to this study).

Only the incident rehabilitation protocol differed be-tween the two trials. During the “control” rehabilita-tion trial, the participants completed a set of standardfirefighting drills in a training structure and then re-moved their helmet, hood, gloves, and bunker coat andsat in a rehabilitation area in a cool room (approxi-mately 20◦C). Participants were provided with waterad libitum. This control condition was meant to re-flect what is typically done at a fire scene—althoughwe recognize there is great variability. During the “en-hanced” trial, the participants completed the same setof firefighting drills and then were required to removeall of their turnout gear (including bunker coat andpants) and consume up to 500 mL of water and atleast 355 mL of a commercially available sport drink(Gatorade, Chicago, IL; 21 g carbohydrate [CHO]), andwere aggressively cooled using cold towels. However,hydration was not withheld from any participants whofelt they needed more, nor was it required of those whodid not feel as if they could consume more. Partici-pants sat in the same area as they did during the con-trol rehabilitation trial. In addition, during the first 10minutes in recovery in the “enhanced” trial, firefight-ers drank 355 mL of a commercially available recoverydrink (Endurox, PacificHealth Laboratories, Matawan,NJ; 20 g CHO, 5 g protein [PRO]).

Experimental Protocol

A schematic description of the timeline for each trialis shown in Figure 1. As outlined in the Measure-ments section, baseline data were collected prior tofirefighting activities. The participants then performedprescribed firefighting drills in full personal protectiveequipment (PPE; including self-contained breathingapparatus [SCBA]), followed by an immediate post-firefighting data-collection session. The postfirefight-ing data collection required approximately 7 minutesto complete; thus to fully account for changes in vi-tal signs throughout the study, separate postfirefight-ing and entry-to-rehabilitation data were collected for

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216 PREHOSPITAL EMERGENCY CARE APRIL/JUNE 2011 VOLUME 15 / NUMBER 2

FIGURE 1. Schematic of study design and timeline. Note that time is not drawn to scale. FF = firefighting; vascular = vascular function based onseveral novel measures.

heart rate, core temperature, and blood pressure. Par-ticipants then underwent rehabilitation for 15 minutes(control or enhanced condition). Next, firefighters per-formed a dummy drag protocol (84 kg; 12 meters; ap-proximately 9 seconds) to assess their ability to per-form a simulated rescue. Following rehabilitation andthe dummy drag, participants changed into dry clothesand walked to an adjacent building (fire station) wherethey remained during the 120-minute recovery period.During recovery, firefighters were in the seated posi-tion and engaged in classroom activities or reading tomimic what may occur at a fire station following a firecall (assuming the suppression crew was relieved ofoverhaul and cleanup duties).

The firefighting drills lasted 18 minutes (requiringapproximately 1 cylinder of air for most participants)and consisted of nine 2-minute periods of alternatingrest and work. The work cycles included stair climb-ing, simulated forcible entry, a simulated search, andsimulated hose advance. The live-fire drills were com-pleted on the second story of a training building. Theselive-firefighting drills were similar to those employedin previously published studies.4,5,11–16

Each participant was paired with a trained memberof the research staff, who safely escorted the partici-pant throughout the protocol. During each test, the es-cort monitored the participant’s heart rate and workcompleted in each cycle. At the conclusion of each sta-tion, the participant rested for 2 minutes in a kneelingposition on the floor as the safety escort demonstratedthe next task.

Three thermocouples were installed in the buildingnear the search station located 0.15 m above the floor,1.2 m above the floor, and 2.4 m above the floor(∼0.3 m below the ceiling) to measure room temper-ature. Type K (Chromel-Alumel) thermocouples withfactory-welded beads were utilized in conjunctionwith a digital data-acquisition system (Omega En-gineering, OM-DAQPRO-4300; Stamford, CT) thatsampled data every 10 seconds. Throughout the burn,

trained stokers controlled the temperature in thetraining structure by monitoring the thermocouplereadings and adding small fuel packages to the firesetssequentially and controlling the ventilation conditionsin the room. The temperatures at the midlevel pointwere maintained at roughly 71–82◦C and the floortemperatures were maintained at 35–41◦C. The pre-scribed firefighting activities required participants towork almost exclusively in the vertical area betweenthe middle and floor thermocouple.

Measurements

Height, weight, body composition/percentage bodyfat (via chest, abdomen, and thigh skinfolds; calculatedusing the Jackson-Pollock 3-site equation17), and fast-ing glucose level and full cholesterol profile from a fin-gerstick sample (Cholestech, Hayward, CA) were as-sessed prior to participating in the live-fire training.

Throughout firefighting, rehabilitation, and recov-ery, body temperature was continuously measuredusing a monitor and a silicone-coated gastrointestinal(GI) core-temperature capsule (Mini Mitter, VitalSense;Philips Respironics, Bend, OR). Participants swal-lowed a small disposable core-temperature-sensorcapsule the night before the study was conducted.Firefighters wore a heart rate monitor throughout thefirefighting and recovery protocol (Polar Electro, Inc.,Kempele, Finland). Blood pressure was assessed viaauscultation immediately before and after firefighting,before and after rehabilitation, and every 30 minutesduring recovery by EMS personnel trained at the emer-gency medical technician (EMT)-basic level or higher.

Applanation tonography was used to assess centralblood pressure and subendocardial viability ratiopre- and postfirefighting activity and during recovery.Radial artery pressure waveforms were attained inthe seated position from a 10-second epoch using ap-planation tonometry and a high-fidelity strain-gaugetransducer (Millar Instruments, Houston, TX). Central

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aortic pressure waveforms were constructed from theradial artery pressure waveforms (SphygmoCor, At-Cor Medical, West Ryde, New South Wales, Australia)using a validated transfer function18 that has alsobeen verified during exercise.19 The subendocardialviability ratio (SEVR) was calculated from the centralaortic waveform as the ratio of the area under thediastolic pressure–time portion of the waveform to thesystolic pressure–time waveform integral. The SEVRis related to heart rate, ejection duration, and arterialload20,21 and provides an estimate of the arterialsystem’s ability to perfuse myocardial tissue in orderto meet the heart’s energy requirements. If the SEVRdecreases from baseline levels, the heart will be facedwith a reduced energy reserve, potentially resultingin lower tolerance for strenuous physical activitiessuch as fighting a fire.22,23 Finally, the rate–pressureproduct (RPP) was calculated as the product of systolicblood pressure (SBP) and heart rate divided by 100.The RPP provides an estimate of myocardial oxygenconsumption.24

Immediately after rehabilitation, the firefighters per-formed a dummy drag task to assess their ability toperform a strenuous activity (e.g., a rescue) after the re-habilitation period.25 In this case, the firefighters wereasked to drag an 81.5-kg manikin across a concretefloor over a distance of 12 m. The time to complete thetask was measured via laser triggering at the start andend of the course.

Analytical Methods

The effect of firefighting activities and incident reha-bilitation interventions on heart rate and core tem-perature measures was examined using a repeated-measures mixed multivariate analysis of variance(MANOVA, 2 [intervention: control, enhanced] × 9[measurement period: baseline, before firefighting,immediately after firefighting, during rehabilitation(entry, exit), and during recovery (30, 60, 90, and120 minutes)]. The effect of the incident rehabil-itation interventions on blood pressure duringrehabilitation and recovery was examined usinga repeated-measures MANOVA (2 [intervention:control, enhanced] × 8 [measurement period: beforefirefighting, immediately after firefighting, duringrehabilitation (entry, exit), and during recovery (30,60, 90, and 120 minutes)]. Vascular function wasassessed as a function of the firefighting activitiesand incident rehabilitation intervention again usinga repeated-measures MANOVA (2 [intervention:control, enhanced] × 6 [measurement period: be-fore firefighting, immediately after firefighting, andthroughout recovery (30, 60, 90, and 120 minutes)]. Theeffects of rehabilitation interventions on subsequentperformance (i.e., time to complete) in a simulatedrescue were compared using a paired t-test.

Data were analyzed using SPSS version 18 (SPSS Inc.,Chicago, IL). Descriptive data are expressed as mean± standard deviation for tables and mean ± standarderror for graphs. Statistical significance was set at p <

0.05 for all analyses.

RESULTS

Table 1 presents descriptive data on the firefighterswho participated in this study. Overall, our partici-pants were relatively young (25.6 ± 5.2 years), appar-ently healthy firefighters. In the control rehabilitationcondition, firefighters consumed 480 ± 182 mL of wa-ter, whereas they consumed 380 ± 192 mL of water and366 ± 83 mL of sports drink in the enhanced condition.

There was a significant time effect (p < 0.001) andcondition effect (p = 0.028) for heart rate. As seenin Figure 2, heart rate increased significantly withfirefighting activity. Heart rate increased from 77.3 ±10.4 b·min−1 prior to entering the training course to161.0 ± 16.4 b·min−1 by the second task (forcible entry)and remained elevated to this level after each subse-quent task (data not shown). Heart rate then decreasedrapidly after completion of the training drill. In the 7minutes between postfirefighting and entry to rehabil-itation, heart rate dropped from 162.0 ± 15.4 b·min−1 to110.8 ± 16.0 b·min−1, but only reduced to 101.5 ± 14.2b·min−1 during the remaining 15 minutes of rehabili-tation. Heart rate remained significanly elevated frombaseline until between 70 and 130 minutes after the be-ginning of the study (30 and 90 minutes into recovery).

Heart rate was significantly higher for firefighters inthe enhanced condition compared with the standardcondition during the recovery period. A post hoc anal-ysis was conducted with a paired t-test at each timepoint and showed that the control and enhanced con-dition trials were not significantly different until therecovery period; however, the enhanced rehabilitationcondition resulted in significantly higher heart ratesat the 70-minute (82.7 ± 8.2 vs. 77.6 ± 9.3 b·min−1)and 100-minute (81.1 ± 10.3 vs. 73.9 ± 10.5 b·min−1)time points (30 and 60 minutes into recovery). Thepost hoc analysis also showed that heart rate returns to

TABLE 1 Descriptive Statistics for the Recruited FirefighterSubjects

Mean (SD) Range

Age, yr 25.6 (5.2) 19–39Height, m 1.81 (0.01) 1.65–1.98Weight, kg 83.3 (11.2) 67.1–111.1Body mass index, kg/m2 25.4 (2.0) 20.6–28.8Body fat,% 15.5 (4.5) 6.0–24.4Total cholesterol, mg/dL 172.2 (36.8) 126–271LDL, mg/dL 106.1 (30.3) 68–195HDL, mg/dL 45.4 (12.7) 24–67

HDL = high-density lipoprotein (cholesterol); LDL = low-density lipoprotein(cholesterol); SD = standard deviation.

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FIGURE 2. Changes in heart rate throughout the test protocol (n = 21). Dotted lines indicate the times when heart rate returns to baseline levels.∗Significant condition affect at these time points. FF = firefighting.

baseline condition (e.g., no longer statistically ele-vated) between 70 and 100 minutes for the standardcondition (i.e., at least 50 minutes after firefighting),but between 100 and 130 minutes for the enhanced re-habilitation condition (i.e., at least 80 minutes after fire-fighting activities have ceased).

For the core temperature data shown in Figure 3,we experienced signficant data loss (n = 12) dueto difficulties in retaining the core-temperature pills.However, there was a significant time effect (p < 0.001)for core temperature, which increased from 37.1◦C ±0.2◦C to 37.8◦C ± 0.4◦C during the short bout of fire-fighting activities. Unlike heart rate, core temperaturecontinued to increase (to 37.9◦C ± 0.4◦C) between theend of firefighting and the beginning of rehabilitation.After this time, core temperature decreased rapidly,but a post hoc analysis again showed that core tem-perature did not return to baseline levels (i.e., did notcease to be statistically elevated) until 100 minutes(60 minutes into recovery). Despite the addition ofactive cooling and complete removal of bunker gearin enhanced rehabilitation, there was no significantcondition effect on core temperature (p = 0.820).

There was a significant time effect for SBP (p <

0.001) and diastolic blood pressure (DBP, p = 0.025)but no significant condition effect for either SBP orDBP (Fig. 4). Prefirefighting SBP averaged 133.9 ±11.4 mmHg, whereas postfirefighting SBP averaged134.2 ± 11.7 mmHg in this group of young, relatively

healthy firefighters. The SBP dropped rapidly duringrehabilitation. On average, the SBP decreased 20.5 ±13.1 mmHg—from 134.2 ± 11.7 mmHg at 18 minutes(immediately after firefighting) to 113.7 ± 10.5 mmHgat 40 minutes (15.2% by the end of rehabilitation). In11 trials, the SBP dropped by more than 20 mmHgduring the rehabilitation period and in four casesthis decrease was larger than 30 mmHg. The aver-age prefirefighting SBP for subjects participating inthese 11 trials was 134.6 ± 13.7 mmHg, which is notsignificantly different from that for the rest of thesample. In the four cases in which SBP dropped bymore than 30 mmHg, the prefirefighting SBP wassignificantly higher compared with that for the rest ofthe population (p = 0.02, 142.5 ± 9.3 vs. 132.9 ± 11.2mmHg). However, there was no correlation betweenthe prefirefighting SBP and the drop in SBP duringrehabilitation (r = 0.096). In fact, in five subjects, theSBP declined by more than 20 mmHg in the first 5minutes of rehabilitation, despite prefirefighting bloodpressures that were, on average, not significantlydifferent from those for the rest of the sample. Afterrehabilitation and the dummy drag, the SBP valuesduring recovery averaged approximately 123.2 ± 10.4mmHg, a recovery of 7.7%, and were stable throughoutrecovery.

As shown in Figure 5, aortic blood pressure followeda similar pattern to peripheral blood pressure obtainedvia auscultation; there was a significant time effect for

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FIGURE 3. Changes in core temperature throughout the test protocol (n = 12). Dotted line indicates the time when core temperature returns tobaseline levels. FF = firefighting.

FIGURE 4. Changes in systolic blood pressure (SBP) and diastolic blood pressure (DBP) throughout the test protocol (n = 20). After the prefire-fighing level, SBP remains reduced throughout the study, whereas DBP remains unchanged. FF = firefighting.

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FIGURE 5. Changes in peripheral and aortic systolic blood pressure (SBP, aSBP) and diastolic blood pressure (DBP, aDBP) throughout the testprotocol. Data from complete sets combined standard and enhanced conditions as there was no significant condition effect (n = 31). FF =firefighting.

aortic SBP (aSBP, p < 0.001) and mean arterial pres-sure (p = 0.001; not shown in Fig. 5) but not for aorticDBP (aDBP), and there was no significant condition ef-fect. Table 2 shows the Pearson correlation coefficientbetween each of the 31 trials at each measurement pe-riod. In each case, the Pearson correlation is significant(p < 0.001) and shows strong correlation (average r =0.928).

As shown in Figure 6, there was a significanttime effect (p < 0.001), condition effect (p = 0.012),and time × condition interaction (p = 0.010) forthe RPP. As expected, the RPP increased signifi-cantly during firefighting activity because of theincrease in myocardial oxygen consumption duringfirefighting. However, the RPP rapidly decreased

below prefirefighting values by the first 30 minutesof recovery. There was a significant condition effect,with the RPP being significantly lower in the controlcondition.

There was a significant time effect (p < 0.001),condition effect (p = 0.002), and time × conditioninteraction (p = 0.048) for the SEVR. The SEVR wassignificantly reduced after firefighting and recov-ered relatively slowly during rehabilitation and intorecovery (Fig. 7).

On average, the firefighters required just over 9 sec-onds (9.1 ± 1.2 sec control; 9.3 ± 2.1 sec enhanced) tocomplete the dummy drag task. There was no signifi-cant condition effect on the time required to performthe dummy drag task, indicating that the ability to

TABLE 2. Peripheral and Aortic Systolic and Diastolic Blood Pressures at Each Measurement Point (n = 31), Presented as Mean(Standard Deviation)

Time (min) SBP (mmHg) aSBP (mmHg) r DBP (mmHg) aDBP (mmHg) r

0 131.7 (10.3) 111.7 (10.1) 0.886 76.5 (7.3) 77.6 (7.5) 0.99618 135.3 (11.0) 114.3 (9.5) 0.935 78.0 (8.3) 81.2 (7.9) 0.98340 113.4 (10.8) 102.2 (10.4) 0.777 74.4 (9.5) 76.3 (10.1) 0.89055 124.5 (10.5) 106.6 (9.4) 0.891 74.0 (7.7) 75.5 (7.6) 0.96170 124.8 (9.2) 105.8 (9.8) 0.933 73.7 (11.4) 75.0 (11.1) 0.994

100 121.3 (12.1) 103.6 (11.6) 0.911 72.9 (10.5) 73.6 (11.0) 0.985130 121.8 (10.8) 104.7 (11.6) 0.901 75.2 (7.7) 75.4 (8.8) 0.906160 123.1 (11.1) 106.5 (12.9) 0.943 74.9 (10.0) 76.3 (9.9) 0.950

The peripheral and aortic values are highly correlated as seen by the Pearson correlation at each time (in all cases p < 0.001).aDBP = aortic diastolic blood pressure; aSBP = aortic systolic blood pressure; DBP = diastolic blood pressure; SBP = systolic blood pressure.

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FIGURE 6. Changes in rate–pressure product (RPP) throughout the test protocol (n = 20). All time points are significantly different from those forthe prefirefighting condition, dropping below this level before the 30-minute recovery time period. ∗Significant condition effect. FF = firefight-ing.

FIGURE 7. Changes in subendocardial viability ratio (SEVR) throughout the test protocol (n = 18). Dotted lines indicate the times when SEVRreturns to prefirefighting levels. ∗Significant condition affect at these time points. FF = firefighting.

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perform high-intensity anaerobic work was not influ-enced by rehabilitation protocols.

DISCUSSION

The major findings of this study are that recovery fromeven a short bout of firefighting activity in healthy rel-atively young firefighters occurs over a much longertime period than is typically provided by incident re-habilitation on the fireground. Furthermore, we docu-mented a significant drop in SBP during rehabilitation,and the magnitude of that drop was greater than whatis normally associated with postexercise hypotension(PEH). Though rehabilitation personnel are often fo-cused on the risks associated with elevated blood pres-sures, the risk of hypotension (i.e., syncope) mustalso be considered. Modifications to current rehabili-tation protocols, including adding active cooling and anutrition intervention, did not provide significant im-provements when rehabilitation was conducted in acool, dry room with an ample supply of water.

Our participants were young, healthy firefighters(Table 1). The mean body mass index (BMI) for thisgroup was between lean and overweight: Eight fire-fighters had a BMI between 20 and 25 kg/m2, whereas12 firefighters fell in the overweight range (25 kg/m2

< BMI < 30 kg/m2). None of the recruited firefight-ers were obese based on BMI. Total mean choles-terol level was in the desirable range; mean low-density lipoprotein (LDL) cholesterol level was in thenear-optimal range and mean high-density lipopro-tein (HDL) cholesterol level was in the average range.Thus, our findings suggest rather drastic changes inheart rate, blood pressure, and body temperature evenin these very healthy individuals.

Heart Rate and Core Temperature

During firefighting activities, heart rates were elevatedat approximately 84% of maximal age-predicted levelsuntil the firefighters exited the burn room. This level ofexertion is commonly seen with firefighter subjects.4,5

However, this study shows that firefighters’ heart ratesdo not return to baseline until approximately 50 to 80minutes after firefighting. Furthermore, the standard(or control) rehabilitation condition appears to allowthe heart rate to return to baseline levels more rapidlyduring the recovery period than during the enhancedrehabilitation condition. At the completion of rehabili-tation, heart rates were not different between the en-hanced and control rehabilitation conditions (92.4 ±9.2 vs. 90.8 ± 8.1 b·min−1, respectively). However, dur-ing recovery, the enhanced condition was significantlyhigher than in the control condition (an average of7.2 b·min−1 higher at 60 minutes into recovery).

Core temperature increased an average of 0.7◦C dur-ing firefighting (rate of 0.037◦C·min−1), which is simi-

lar to that measured during previous studies of similarduration.4,5,26 While this magnitude of core tempera-ture increase would suggest mild hyperthermia, themost significant concern is with the rate of rise, whichcan rapidly reach a level of severe hyperthermia ifmultiple cylinders of air are consumed prior to rehabil-itation. The rate of core temperatue rise is also similarto what Romet and Frim (1987) have reported, thoughthey suggested that the rate of rise in core temperatureduring firefighting is affected by the activity of the fire-fighter, with the nozzleman’s (lead hand’s) having thegreatest rate of rise.26 During the first 7 minutes afterfirefighting, core temperature continued to rise at a rateof approximately 0.020◦C·min−1 despite removal of thebunker coat. This finding is consistent with previousresearch documenting that core temperature continuesto rise after the cessation of exercise or work in protec-tive clothing and following firefighting activities.4,5,27

Once core temperatures peaked, they declined rapidlyduring the first few minutes of rehabilitation. How-ever, we found that core temperature did not returnto baseline until approximately 50–80 minutes afterfirefighting, and this outcome was not improved byproviding active cooling during rehabilitation.

The effectiveness of different rehabilitation inter-ventions in lowering core temperature has been asubject of much debate in the fire service and amongresearchers.7,8 Two previous studies in which fire-fighter cooling protocols were assessed suggested thatactive cooling is more effective than passive cooling 1)in increasing tolerance time and total work time afterfirefighters worked in an environmental chamber7

and 2) in reducing core temperature after conductingcontrolled live-fire training.8 Espinosa and Contreras(2007) also studied several different active coolingstrategies and suggested the use of cold towels wasas effective as other techniques, yet operationallymore feasible.8 A recent study in which Hostler et al.compared active cooling devices with passive coolingafter repeated work bouts involving walking on atreadmill while wearing PPE found that active coolingdid not enhance firefighter recovery over passivecooling under moderate ambient conditions (24◦C).28

These authors also reported that 20 minutes was nota sufficient amount of time to permit core temperatureto return to baseline following 50 minutes of walkingin PPE. In the current study, we did not find a signif-icant improvement in heart rate or core temperaturerecovery when using cold towels compared withpassive cooling. Differences in ambient temperaturemay help explain the seemingly contrary results inthe studies above. In the current project, rehabilitationwas conducted in a room with ambient temperaturesbetween approximately 18◦C and 21◦C and thus pas-sive evaporative cooling could take place. Similarly, inthe study conducted by Hostler et al., the ambient tem-perature averaged 24◦C; thus, the participants could

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effectively cool themselves during the rehabilitationperiod. On the other hand, the studies by Selkirk etal.7 and Espinosa and Contreras8 were conductedunder high ambient temperatures (35◦C, 50% relativehumidity [RH]7; 29◦C, 46% RH8). Under these condi-tions, evaporative cooling is limited and active coolingappears to confer an advantage over passive cooling.Thus, environmental conditions are an importantfactor that must be considered when determiningwhether to provide active or passive cooling.

Blood Pressure

A single bout of moderate-intensity exercise lasting30–60 minutes typically produces postexercise SBPreductions of approximately 5–10 mmHg, which isthe phenomenon known as postexercise hypotension(PEH).29 The firefighters in the present study exhibitedreduced SBP following firefighting, consistent withdata on PEH. The reduction in SBP in the firefight-ers immediately after firefighting (22.5 mmHg) wasconsiderably greater than expected, especially consid-ering that the active firefighting lasted only 18 min-utes. Postexercise hypotension is thought to be causedby a reduction in vascular resistance, mediated bychanges in the autonomic nervous system and va-sodilator substances.30 Work in hot environments or inPPE can exacerbate PEH because of loss of plasma vol-ume and a greater drop in vascular resistance due tovasodilation of the cutaneous circulation.31

Even after SBP increased slightly during recovery,it remained lower than expected. In 17 of the 42observations made in this study (40.5%), the differ-ence between postfirefighting and recovery SBP val-ues was greater than 10 mmHg, and in six of the 42cases (14.3%), the difference in SBP was greater than20 mmHg. One individual whose prefirefighting SBPwas 157 mmHg had a drop in SBP from 153 mmHg to106 mmHg in the first 5 minutes of rehabilitation; hisSBP remained at approximately 110 mmHg through-out rehabilitation, and then returned to approximately122 mmHg and remained constant during the last 90minutes of recovery.

Following rehabilitation and the simulated rescue,the mean SBP increased to approximately 120 mmHgand remained remarkedbly stable at this level until theend of the recovery period. This value is still consid-erably lower than the prefirefighting blood pressure,thus it appears that even short-term firefighting pro-duces substantial PEH for a prolonged period. Thisis again consistent with the PEH typically reportedfollowing aerobic exercise. Moderate-intensity exerciseand high-intensity exercise have been shown to re-sult in similar levels of PEH.32 What is novel aboutour findings is the more exaggerated reduction in SBPobserved during the rehabilitation period (in the 15-minute period after firefighting) compared with the

recovery period. These findings also suggest that thelocomotion after rehabilitation (during the simulatedrescue) may have increased venous return and/or pro-duced some vasoconstriction leading to a slight in-crease in blood pressure, which was then maintainedfor the duration of the recovery period.

It is well established that PEH is greater in peoplewith high blood pressure compared with normoten-sive individuals.33 Our prefirefighting values suggestthat our average participant was prehypertensive, andthis may have contributed to the greater-than-expectedreduction in blood pressure. However, it is also possi-ble that our preactivity blood pressure values reflectsome anticipation about the firefighting activity thatthe participants were about to undertake, and thus donot represent true baseline blood pressures.

Elevated blood pressure at rest is an established riskfactor for future cardiovascular events.34 Furthermore,an exaggerated blood pressure response to exercisestress is a strong predictor of cardiovascular mortal-ity from myocardial infarction and stroke.35,36 CurrentNPFA guidelines (NFPA 1584) recommend monitoringblood pressure during incident rehabilitation.1 Whilethere are well-established guidelines detailing whatconstitutes an exaggerated blood pressure response toa standardized exercise stress test (SBP > 250 mmHg orDBP > 150 mmHg37), there is a paucity of data avail-able regarding normal blood pressure responses to thestress of firefighting. Futhermore, while elevated bloodpressure following firefighting is undoubtedly of con-cern, our data suggest that EMS personnel overseeingmedical monitoring of firefighters during rehabilita-tion should also be concerned about hypotension andthe attending risk of syncope.

Central aortic blood pressure may be a better pre-dictor of clincial outcome than is brachial pressure.9,10

Aortic blood pressure values in this study followed asimilar pattern to that of blood pressure obtained viaauscultation, but, as expected, the aortic SBPs wereconsiderably lower than those obtained via auscul-tation. In our study, the central and brachial bloodpressures mirrored each other throughout the rehabil-itation and recovery period, suggesting that brachialblood pressure is an adequate method of blood pres-sure monitoring following firefighting.

Myocardial Oxygen Supply and Demand

The decrease in SEVR immediately after firefightingreflects a decrease in myocardial perfusion relative tocardiac workload, whereas the significant increase inRPP reflects an increase in the myocardial tissue de-mand for oxygen. However, as Figure 6 shows, the RPPrapidly returns to levels below prefirefighting valuesby the first recovery time period. As the prefirefight-ing RPP levels may be slightly elevated from baselinebecause of increase in heart rate at the preactivity time

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point and the RPP remains relatively stable through-out recovery, it is expected that the RPP has recov-ered to near-baseline levels by this time period. How-ever, the SEVR does not return to prefirefighting levelsuntil some time between the 30- and 60-minute timepoints for control rehabilitation and between 60 and90 minutes for enhanced recovery. Thus, even thoughthe myocardial demand for oxygen rapidly returnsto baseline levels, the subendocardial perfusion re-mains reduced for another 30–90 minutes. Additionalresearch is needed to determine whether a reducedSEVR during recovery may be related to an increasedvulnerability to sudden cardiac events or whetherthere is in fact a balance between oxygen supply anddemand.

LIMITATIONS

Several limitations may have affected our results. First,this study used simulated firefighting activities in atraining structure that contained live fires. This situ-ation is less dangerous and thus less stressful than ac-tual firefighting activities. As such, our results likelyunderestimate the actual cardiovascular strain associ-ated with firefighting activity. Also, our prefirefightingactivity measurements may reflect an anticipatory re-sponse on the part of the participants as they mentallyprepared for the firefighting activity. Thus, our pre-firefighting activity values may not reflect true “rest-ing” values. Additionally, we did not control the fluidintake during the control trial in which participantshad ad libitum access to fluids. This resulted in par-ticipants’ consuming different amounts of fluids in thetwo trials.

CONCLUSIONS

This study examined the acute effects of firefightingon traditional vital signs and novel vascular mea-sures, documented the time course of recovery, andcompared two incident rehabilitation strategies to de-termine the extent to which an “enhanced” reha-bilitation might facilitate recovery from firefightingactivities.

Our study involved a sample of young, healthy fire-fighters who were immediately removed from the fire-fighting activities into a controlled, relaxed environ-ment. The firefighters were provided with 15 minutesof rehabilitation prior to completing a 10-second simu-lated rescue task and then recovered for 120 minuteswithout physical or psychological interruption. Thisscenario represents a likely best case. Often firefight-ers will return to firefighting work after consumingone cylinder of air. Then, once the firefighting opera-tion has ended, they will be involved in overhaul andcleanup operations, which may further exacerbate theperturbations measured and the time rate of recovery.

Keeping in mind the points made above, several im-portant conclusions can be drawn from this study re-garding the effect of firefighting activities on the car-diovascular system and the time rate of recovery ofseveral important measures.

� Firefighting activities resulted in a significant eleva-tion of core temperature and heart rate. Importantly,the recovery from these effects occurred over a timecourse of hours, even after a short bout of firefight-ing in this young, healthy sample of participants.

� The SBP values displayed a significant and rapid de-cline shortly after firefighting activities and into therehabilitation period. During recovery, the SBP in-creased above its nadir but remained lower than pre-firefighting levels for at least 120 minutes. This find-ing is consistent with PEH responses seen duringa bout of high-intensity aerobic exercise. However,in this group of young, healthy firefighters, therewas wide variability in the blood pressure responseto firefighting and the recovery from firefighting.While firefighters are often concerned about ele-vated blood pressures, this study suggests that fire-fighters should be aware of the potential dangers ofhypotension during rehabilitation and recovery aswell.

� Aortic blood pressure responses very closely matchblood pressure values determined via auscultation.

� Depressed SEVR measurements imply that firefight-ers may have a reduced subendocardial perfusionfor up to 110 minutes after an initial firefighting ac-tivity has ceased.

� The enhanced rehabilitation condition appeared tohave little effect on physiologic recovery under themoderate environmental conditions in this study.The rehabilitation conditions had no effect on coretemperature, suggesting that the cooling portion ofthe intervention had no effect when rehabilitationwas conducted in a cool room. The rehabilitationcondition also had no effect on firefighters’ abilityto conduct a postrehabilitation simulated rescue asmeasured by a dummy drag protocol.

References

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2. Fahy RF, LeBlanc PR, Molis JL. Firefighter fatalities in theUnited States in 2008. NFPA J. 2009;103(4):60–7.

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